Fuel burner control system



Feb. 24, 1942. w soN I 2,274,177

. FUEL BURNER CONTROL SYSTEM Filed Dec. .9, 1940 INVENTOR John... M.WiI Ls n..

v ATTORNEY Patented Feb. 24, 1942 FUEL BURNER coN'rno'r. SYSTEM John M. Wilson, Minneapolis, Minn assignor to Minneapolis-Honeywell Regulator Company, I Minneapolis, Minn, a corporation of Delaware Application December 9, 1940, Serial No. 369,241

, J Claims. This invention relates generally to automatic control systems for fuel burners, and more particularly to that'type of system. having a timed automatic safety switch for shutting the system down in the event that combustion is not established within a predetermined time following a demand for heat as evidenced by the closing of a main switch to the system.

In prior art systems wherein two or more electromagnetic relays are utilized in order to get applicable to the control of other types of burners, such as gas, powdered coal, etc.

Referring to the drawing the reference numeral l0 indicates a room thermostat in the form of a bimetal coil being fixed at one end and carrying at its free end a pair of resilient contact blades II and I2. These blades are so related to the stata'tinary contacts l3 and [4 that e on cooling of the bimetallll the blade II will first the proper sequencing and safety functions, the

safety switch actuator (usually an electric heater) is connected directly in series with one of the relays. This is customarily the first relay to be energized upon a demand for heat. In view ot the fact that the current flow through the theater is limited by the reactance of the relay coil, the resistance of theheater must be fairly high in order to develop sufficient heat to give.

the safety switch the proper timing. A high resistance inthe safety switch heater limits the pull-in voltage available for the relay, thus making it diflicult in many instances to obtain the proper relation between the resistance of the heater and the number of turns in the relay coil.

It is an object of the present invention to obviate the above difliculty by energizing the relays substantially simultaneously and directing the current from both of them through the safety switch heater This will materially increase the current flow through the heater with the result that the resistance of the heater may be reduced to substantially a quarter of the value required if only one relay is connected in circuit with it. Obviously, this will materially reduce the voltage drop across the heater and a much higher pull-in voltage for the relays is available.

A further objectisto provide a-system of the above type in which one relay controls an ignition device and the other relay controls the fuelfeed- ,ing device, the arrangement being such that both engage contact l3 and shortly thereafter the blade l2 will engage the contact l4. An electrical resistance element I5 is positioned to afiect the temperature of the bimetal ill in a manner to be described later. v

Indicated generally at 20 is a cold contact assembly and 2| indicates a hot contact ssembly. The cold contact assembly comprises t ree contact blades 22, 23, and 24 which are normally biased to open circuit position that" is, when they are not, acted onby any external forces the blades 23 and 24 will move to the left as a result of a biasing force so that the blades 24 and 23, as well as 23 and 22, will be out of contact with each other. The hot contact assembly comprises two contact blades 25 and 26 which are also normally in open circuit position as shown in the drawing.

These contact assemblies are adapted to be 0D- erated by means of a combustion responsive elee ment which may be of any desired form but which is preferably in the form of a W-shaped bimetallic element 28, which is positioned to respond to the temperature of combustion and is usually placed in the stack. This element forms no part of the present invention but is preferably I ,in the form shown in the patent to Willis H.

Gille No. 2,196,671. One end of the element 28 4 is connected to a fixed part as shown at 29 and relays are energized substantially simultaneously and the first relay is dropped out upon the establishment of combustion to deenergize-the I ignition device while the second relay is held in through a closed hot combustion switch. Other objects reside in the various details of the circuit arrangementwhich are described in the following specification, reference being had to the single figure of the drawing which illustrates, schematically, an oil burner control system embodying-my invention.

In the following description the control system will be referred to as controlling an oil burner the other end is adapted to move in-astraight line and actuate. the rod 30; 'Two slip friction elements 3| and 32- are mounted on the rod 30, the element 3| actuating the hot switch 25, 26

and the element 32 actuating the coldswitches 22,.

23 and 24. The elements iii and have'been i1- lustrated more or less diagrammatically but preferably take the form of clutch type slip friction elements as shown in my co-pending application, Serial No. 260,071.

e As the element 28 expands on an increase in temperature, it moves the rod 30 to the left as shown in the drawing and the slip friction element 31 first engages the blade 25 and moves it into electrical contact with the blade 26. Further movement of the rod 30' to the left will not have although it will be appreciated that it is equally any eil'ect upon the-element 3| "which will merely slide with respect thereto. The movement of the rod 30 also carries the slip friction element 32 which in the position shown in the drawing is holding the cold switches 22, 23 and 24 in closed circuit position. As the rod 36 moves to the left, it first permits-blade 23 to separate from blade 22 and thereafter permits the blade 24 to separate 25 and 26 have separated, the element 3| engages the stop 36 after which the rod 30 slips with respect tothis element.

It will therefore be seen that due to the slip friction connection between therod 30 and the elements 3| and 32 that the hot and cold switches are-actuated by a reverse in temperature changes and are not-dependent upon the establishment of any definite temperature value. The switches are so arranged that on heating, the hot switch 25, 26 will always be closed prior to the opening of the switch 23, 24 and on closing the hot switch 25, 26 will open prior to the closing of the switch 23, 24. In other words, these switches overlap on heating but not on cooling.

This control system is provided with two electro-magnetic relays indicated at and 4|. The

relay 4|] when energized moves the switch blades 42, 43, 44 and 45 to closed position, and the relay 4| whenenergized moves switch blades 46, 41, 48 and 49 to closed position.

The reference numeral 50 indicates generally the usual type of safety switch which is biased to open circuit position but which is latch-closed by means of a thermal element which is the element 5|. As shown, the thermal switch comprises a switch blade 52. dicates the safety switch heater which is adapted to heat the thermal blade 5|, andafter a predetermined period of time to cause it towarp sufiiciently to release the safety switch for movement to open position.

The ignition device is indicated diagrammatically at 55. This device may take the form of a spark transformer, or a hot wire igniter or any equivalent means for igniting fuel. The reference numeral 56 indicates an electrical device for controlling the feed of fuel and may be an electrically operated valve, or may take the form of the usual oil burner motor or any equivalent device. a

The reference numeral 53 in- Electrical energy is supplied to the system. by

means of the line wires 6|! and 6|. across which the primary winding 62 of the step-down transformer is connected. The room thermostat and relays are in the low voltage circuit which is supplied with power from the secondary winding 64 of the transformer 63.

' Operation The system is shown in the drawing with the parts occupying the position which they will occupy when the'room thermostat II is satisfied and has been satisfied fora suflicient length of time to permit the hot combustion witch to open and both of the cold combustion switches to close. Under these conditions both of the relays will be deenergized as the circuit to the secondary 64 is opened at contact |3. The burner motor 56 and ignition device 55 will therefore be deenergized and the entire system will be at rest. Under these conditions the temperature in the room will begin to drop and the bimetallic thermostat ID will first cause the switch blade I to engage the stationary contact I3. This will have no effect upon the system at this time due to the fact that the switch blade 48 and the contact blade l2 are both in open circuit position. On a further decrease in room temperature the thermostat III will move the switch blade l2 into engagement with the stationary contact M. This will result in the energization of relay 40 through the'following circuit: from one side of the secondary winding 64 through conductor 10, contact l3, switch blades H and I2, contact l4, conductors 1| and 12, safety switch heater 53, conductors I3 and i4, cold combustion switches 22, 23 and 24, conductor 15, relay winding 40,

conductors 69 and 16, safety switch 52 and conductor 11 back to the other side of the secondary .64. It will be noted that the energization of this relay is impossible unless both of the cold combustion switches are closed. It is the operation of these switches therefore that times the recycle in this system.

The energization of the relay 40 results in switch blades 42, 43, 44 and 45 moving to closed circuit position. When the switch blade 45 moves to closed circuit position, it establishe the following circuit to the ignition device: from line wire 60 through conductors 18 and 19, switch blade 45, conductor 30, ignition device 55 and conductors 8| and 82 back to the other line wire 6|. The closure of the switch blades" and 43 results in the establishment of a parallel circuit through the relay 4|! shunting the cold switch 22.

23. This circuit may be traced from conductor 13 through conductor 83, switch blades 42 and 43 and conductor 64 to cold switch 23, 24 and hence through the relay 46. This circuit is set up so' that the opening or chattering of the last to close cold switch 22, 23 will not drop out the relay 40. Closure of switch blade 44 results in the energization of relay 4| through the following circuit: from one side of the secondary windin 64, through conductor 10, contact l3, switch blades H'and i2, contact l4, conductor 12, safety.

switch heater 53, conductors 13 and 83, switch I blades 42 and 44, conductors 85 and 86, relay winding 4|, conductors 88 and 16. safety switch 52 and conductor 11 back to the other side of the secondary winding 64. It will thus be seen that the safety switch heater 53 is connected in series I with both of the relay windings 42 and 4| and that these two winding are connected in parallel with'each other.

Energization of the relay winding 4| results in the closure of switch blades 45, 41, 48 and 49. The closure of the switch blade 49 establishes the following circuit throughburner motor 56:

from one line wire ill through cnoductors 16 and 96, switch blade 43, conductor 3|, burner motor 56 and conductors 92 and 82 back to the other line wire 6|. Inasmuch as both the burner motor Q and ignition device have now been energized combustion should be established.

The closure of switch blades 41 and 48 result in closure of a parallel circuit through the relay winding 4| independent of the room thermostat switch I2, 14. This circuit may be traced from one side of thesecondary winding 64 through conductor 'll, contact l3, switch blade bia 2,274,177 metallic element It, conductor 93, electric heater I5, conductor 94, switch blades 48 and 41, conductors 95 and (2, safety switch heater 53, condoctor I3 and 83, switchblades '42 and 44, conductors 85 and 86, relay winding 4| and thus back to the other side of the secondary 54 through thesafety switch 52. It will be noted that this parallel circuit for the relay winding 4| also passes through the safety switch heater 53 so that this heater still carries the current for both of the relay windings. The purpose of this circuit is to shunt the thermostat switch I2, |4 so that if this switch should open slightly due to vibration or other circumstances the relays 40 and 4| will not be dropped out. After the thermostat switch |2 and I4 is definitely moved have moved to closed position.

the room thermostat switches ll, I3 and l2, l4 The closure of the cold switches-22, 23 and 24 is relied upon to provide the proper scavenger period following a flame failure or a power failure. It will be realized that the relay 4| will also drop out on a to open circuit position due to an increase in room temperature, the electric heater I5 is brought into the circuit and heats the thermostat ill in order to raise its temperature slightly above the room temperature in a manner to anticipate the rise in room temperature due to the energization of the burner. The burner will therefore be deenergized prematurely for the purpose ofp-reventing over-shooting of the room temperature.

After combustion has been established the hot combustion switch 25, 26 will be moved toclosed,

position by the slip friction element 3| in the manner already described. This. will establish cluctor 85, switch blades 44 and 43, conductor 84, cold switch 23, 24 and conductor 15, and the circuit for the relay winding 4| goes directly through the conductor 85. Therefore as soon as combustion has been established, as indicated by the closure of the hot combustion switch, the

safety switch heater is immediately shunted out of the circuit. On further increase in combustion temperature the cold switch 22, 23 will open if it has not already done so. This will have no effect upon the system in view of the fact that a, holding circuit for the relaywinding 40 has already been established through cold switch 23, 24. A further increase in combustion temperature will result in the cold switch 23, 24 moving to open circuit position. this switch is directly in series with the relay winding 40, it will deenergize this relay and the switch blades 42, 43, 44 and 45 will 'move to open circuit position.

power failure and cah-not be pulled in again until the combustion switches are 'in closed position.

If during the starting cycle ignition is not obtained the hot combustion switch 25, 26 will remain open and hence the safety switch heater .53 will remain energized. After a predetermined period of time (usually about ninety seconds) the heater 53 will have heated the thermal element 5| sufliciently for it to trip and release the safety switch 52-for movement to open circuit position. This switch must be manually reset before the system can again attempt to start.

It will be seen therefore that this system has been designed to provide all of the usual features of safety and that the main object of the invention has been attained by passing the current of both relay windings through the safety switch 'heater so that the resistance value of this heater may be materially reduced to increase the pull-in voltage of the relays.

Various changes and modifications of this invention may occur to those who are skilled in the art, and I therefore wish it to be understood that I intend to be limitedonly by the scope of the appended claims and not by the specific embodiment of the invention which I have disclosed herein.

I claim as my invention:

1. A fuel burner control system comprising in combination, an electrical fuel feeding device, first and second relays, a normally closed safety switch in control of said relays, an actuator which when energized for a predetermined period. of.

time causes said safety switch to open, a circuit for said first relay including a main switch and said safety switch actuator, a circuit for said second relay including said main switch, said safety switch actuator and a switch which is closed when said first relay is energized, means actuated by said second relay upon energization for rendering said electrical fuel feeding device operative to deliver fuel to apoint of combustion,

I means establishing a shunt circuit around said The opening of 'the switch as will-result in the deenergization of the ignition device 55. The opening of the switches 42, 43 and 44 will have no effect upon the system in view of the fact that the relay winding 4| is now held in by acircuit extending through, the switch blades 43 and 45 and the hotcombustion'switch 25, 25. This is the running condition of the system. a

It will be-noted at this point that inasmuch as the relay 4| is held in through the room thermostat switch l, l3 and thehot combustion switch 25, 26 that either a flame failure-or a movement of the thermostat II to satisfied condition will deenergize the relay 4|. After web deenergization. the system cannot restart untib.

both of the cold switches 22, 23 and 23, llfhav'e been moved closed position and until bothof.

first relay switch whereby said second relay will remain energized independently of said first vrelay, and means opening the circuit to the first relay and safety switch actuator in response to [the establishment of combustion.

.-2. A fuel burner control system comprising in combination, an electrical fuel control device, means for igniting the fuel. first and second relays; a normally closed safety switch in control 0f said relays, an actuator which when energized for a predetermined period of time causes said safety switch to open; a circuit for said first relay including a main switch'and said safety switch actuator, a circuit. for said second relay including said main switch,- safety switch actuator, and a switch'which is closed when said first relay" is energized, a switch closed upon en- 'ergization 'ofsaid first relay for'energizing said ignition means, aswitch closed upon energization of sa'id second relayfor energizing said fuel control device,.means-operating in response to combustion for establishing 'a. parallel circuit to. said second relay independent of said first relay switch and the actuator for said safety switch,

and meansfor subsequently opening the circuit to said first, relay and actuator 'for the safety switch and consequently deenergizing the ignition means. I

3. A fuel burner control system comprising in combination, an electrical fuel control device,

means for igniting the fuel, first and second relays, a normally closed safety switch in control of said relays, an actuator which when energized for a predetermined period of time causes said safety switch to open, a circuit for said first relayincluding a main switch and said safety switch actuator, a circuit for said second relay including said main switch, safety switch actuator, and a switch which is closed when said first relay is energized, a switch closed upon energization of said first relay for energizing said ignition means, a switch closed upon energization of said second relay for energizing said fuel control device, means operating in response to combustion for establishing a parallel circuit to said second relay independent of said first relay switch and the actuator for said safety switch, and means also operating in response to combustion for subsequently opening the circuit to said first relay and actuator for the safety switch and consequently deenergizing the ignition means.

4. A fuel burner control system comprising in combination, an electrical fuel feed control device, means for igniting the fuel fed by said device, first and second relays, a normally closed safety switch controlling the flow of electrical energy to said relays, an actuator which when energized for a predetermined period of time causes said safety switch to open, a circuit for said first relay including a main switch; said safety switch actuator,. and a closed cold combustion responsive switch, a circuit for said second relay including said main switch, safety switch actuator, and a switch which is closed when said first relay is energized, a switch closed upon energization of said first relay for energizing said ignition means, a switch closed upon energization of said second relay for energizing said fuel control device, means operating in response to combustion for establishing a parallel circuit to said second relay independent of said first relay switch and the actuator for said safety switch, said cold combustion responsive switch opening subsequently to deenergize said actuator for the safety switch and said first relay and hence said ignition means.

5. A fuel burner control system comprising in combination, an electricaljuel feed control device, means for igniting the fuel fed by said device, first and second relays, a normally closed safety switch controlling the fiow of electrical energy to said relays, an actuator which when energized for a predetermined period of time causes said safety switch to open, a circuit for Ill said first relay including a main switch, said safety switch actuator, and first and second switches which are closed sequentially in response to a decrease in combustion temperature, a holding circuit closed by said first relay through the last to close combustion switch but independent of said first to close combustion switch, a circuit for said second relay including said main switch, safety switch actuator, and a switch which is closed when said first relay is energized, a switch closed upon energization of said first relay for energizing said ignition means.

a' switch closed upon energization of said second relay for energizing said fuel control device, means operating in response to combustion for establishing a parallel circuit to said second relay independent of said first relay switch and the actuator for said safety switch, said last to close combustion switch subsequently opening to deenergize said safety switch actuator, firstrelay, and ignition means.

JOHN M. WILSON. 

